1. Field of the Invention
The present invention relates to a rotor with a plurality of permanent magnets secured on a rotary shaft. It also relates to a method of manufacturing the rotor and to a motor using the same.
2. Discussion of the Related Art
Heretofore, there has been a known an electric motor as described in Japanese unexamined, published patent application No. 6-284650 (1994-284650). In the motor, a plurality of permanent magnets are circumferentially arranged and secured by gluing to the external surface of a rotary shaft, and a cylindrical cover whose internal surface is slightly larger than a diameter defined by the external surfaces of the permanent magnets is fit on the external surfaces of the permanent magnets in order that the permanent magnets can be prevented from scattering when separated from the rotary shaft or broken. In the manufacturing of the motor, a freely rotatable roll is brought into alignment with an axial flute or groove which extends at a juncture portion of every two adjoining permanent magnets and is axially moved along the axial groove while being pressed on the external surface of the cylindrical cover, whereby the same is plastically deformed to be bent into the axial groove, thereby having the internal surface fit tightly on the external surface of the permanent magnets.
The permanent magnets are fragile, and therefore, when the roll is moved along the axial groove formed at the juncture portion of every two adjoining permanent magnets as it is pressured into the axial groove, it often occurs that the permanent magnets are broken or damaged due to a large force acting thereon.
It has also bee practiced to adhere and secure the cylindrical cover to the rotary shaft with an adhesive. Adhesives are generally liable to suffer the environmental influences such as, for example, temperature, humidity, or the like and are difficult to be kept constant in quality. This gives raise to a drawback that where such an adhesive is used, the time to manufacture the motor is extended and the manufacturing cost is increased. Moreover, as the performance of the adhesive is deteriorated due to the thermal influence, the cylindrical cover gets out of place, whereby it cannot perform the function to prevent separated permanent magnets or broken fragments thereof from scattering.